Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge control surfaces are used to control the wing coefficient of lift. The leading edge control surface is known as a slat and a trailing edge control surface is known as a flap. During normal flight the slats and flaps are retracted against the leading and trailing edges of the wing, respectively. However, during take-off and landing they are deployed from the wing so as to vary the airflow across and under the wing surfaces. By varying the extent to which the slats and flaps are deployed from the wing, the lift provided by the wing can be controlled. Other trailing edge control surfaces include ailerons and spoilers.
The control surfaces are moved using hydraulic actuators mounted within the wing structure and coupled at each end to the wing and to the control surface via spherical bearing assemblies at both ends of the actuator.
As demands for thinner, more efficient wing profiles increase, it becomes increasingly difficult to fit all the necessary systems, structure and actuation devices within the wing outer mould line and the size of actuator that may be employed for controlling deployment of various control surfaces is severely limited. In particular, the length of conventional hydraulic cylinders is a problem, especially as the spherical bearing at each end of the actuator each add between 50 to 200 mm to the length of the actuator which is often unacceptable due to the tight space constraints within the wing structure.
To address the problems referred to above, it is known to employ trunion mounted cylinders as these are shorter in length. However, as these actuators rely on only one spherical bearing at the moving end of the hydraulic cylinder, the fixed end of the actuator is mounted for movement about one axis, and so they suffer from high wear on the cylinder bushes and seals resulting in premature failure due to hyperstatic loading caused by wing bending and manufacturing tolerances. Therefore, regular inspection and maintenance is necessary to avoid a potential failure.
It is therefore desirable to provide an assembly in which the actuator is mounted via a spherical bearing at both ends but which does not have the additional length suffered by conventional bearing assemblies. Embodiments of the present invention therefore seek to provide an actuator which substantially overcomes or alleviates the known problems with conventional bearing assemblies and to provide an actuator of reduced length that can withstand hyperstatic loads caused by wing bending.